An example of a ballpoint pen tip used as a writing tip of a ballpoint pen is formed by cutting a cylindrical metal material. In such a ballpoint pen tip, a writing ball is inserted into a ball house formed in its front end, and then its front edge is bent inwardly by press deformation to hold the writing ball.
Ink for a ballpoint pen includes oil-based ink and water-based ink. The water-based ink generally has a lower viscosity than that of the oil-based ink, and thus, if the writing tip is held downward, so-called “bleeding” may occur that is a phenomenon in which the ink is lowered by gravity and leaks from the writing tip. When the ballpoint pen is clipped to a breast pocket of clothes, the ink leaks by this phenomenon to dirt the clothes. Such a phenomenon particularly becomes a problem in a ballpoint pen such as a so-called retractable ballpoint pen in which a writing tip is always open without being covered with a cap and the writing tip is almost always kept downward both while being used and while not being used.
Thus, particularly in a retractable ballpoint pen using water-based ink, as in the techniques described in Patent Documents 1 and 2 below, a spring is mounted in a ballpoint pen tip, and a writing ball is always pressed toward a front end and biased to block a clearance between the writing ball and a bent portion, thereby preventing the bleeding. Moreover, as in the technique described in Patent Document 3 below, an elastic body is inserted instead of the spring to achieve the same advantage.
Further, a conventional technique including a three-step tapered portion in a writing tip is described in Patent Document 4 below.
Patent Document 1: JP 10-329475 A (FIGS. 1 to 3)
Patent Document 2: JP 2002-200877 A (FIG. 2)
Patent Document 3: JP 3156988 B (FIG. 1)
Patent Document 4: WO98/030401 (re-publication of Japanese Patent Application No. 10-530728)